Thursday, March 31, 2016

Last burn of season at Pleasant Valley Conservancy

We did savanna/prairie/wetland burns on Tuesday March 29, 2016. These were the last burns of the spring burn season. The other burns were done on March 11 and March 21.

This is the earliest we have ever finished our burns. This year they were mostly done on
fairly cool days when there was a high pressure air mass over the area. Temperatures
never got above 60, RH generally in the 40s, wind moderate. The new burn permitting program established this year by Wisconsin DNR Forestry worked very well.

Today the wind was out of the south or east, gusting to 7-8
mph. RH got down to about 40 in mid afternoon, but there was dew on the grass in
morning with a temperature of 31 F.

Long-narrow savanna burn: Because the wind was out of the SE, we started lighting at the
west end of Unit 19. This is a long narrow savanna of about 5 acres that is situated between the ridge-top savanna and the north woods. The North Firebreak separates this unit from the big woods. To protect the North woods, lighting began on
the NW corner, with one drip torch and several waters along the North Firebreak and a second drip torch doing interior lighting around special trees to be protected. [I will have a discussion of tree-centered burning in an upcoming blog post.] The north line
moved first.

Starting the burn at the west end of the long narrow savannaNote the large bur oaks. This is an area with many venerable trees

A second (south) single drip torch line starting at the same location lighted the whole length of the unit along the gravel road. See photos. Because of the south-easterly wind, this second line was mostly a headfire,
although the interior lighting mentioned above created some backfire. (Remember that the extensive savannas across the gravel road were already black from the March 21 burn.)

Bringing the fire line along the savanna. The savanna to the right had been burned 3-21-2016

Because of the long burn line, and the need to protect
trees, this burn moved fairly slowly and probably took most of an hour to do.

Close to the end of the narrow savanna. The smoke in the distance is from the line on the North fire break.

The pumper unit was used to put out some burning snags and downed trees, especially in an area where a patch of dead black oaks still remained. (See photos) These trees had been killed by oak wilt about 10 years ago and many of them had been "topped" by a derecho (straight-line tornado) that ran along the top of the ridge about 5 years ago. The downed timber had by now become quite rotted, which meant it caught fire easily. After the burn was completed a three-person crew returned to this site and cut up the burning wood so that it could be sprayed by water from the pumper unit. (See photos)

[Trees in the black oak group have open woody structure, which means they are very sensitive to decomposition. The white oak group, which includes bur oak, have their pores plugged with tyloses, making them highly resistant to decomposition. Oaks in the white oak group can lay on the ground for many years without decomposing but those in the black oak group decompose rapidly.]

Using the pumper unit to put out the fire on a dead stump next to a living white oak.Because of the large amount of wood in this savanna, there is often a lot of mop-up.Note that this whole unit is black, indicating a satisfactory burn.

Prairie/oak-woodland burn: Once this savanna area was secured, we moved on to Toby’s Prairie and the
Woodland Extension which extends into the North woods. Lighting began at the NW corner of the Woodland Extension
and moved east along the edge of the woods. A second drip torch did interior lighting along
the N edge of Toby’s once the Woodland Extension black line was secure. This
was done in order to speed up the burn, although the Woodland Extension burn would probably have eventually reached and started Toby’s on fire.

A second line started
at the NW corner and moved up (South) along the Woodland Extension and then
along the narrow West side of Toby’s. Eventually, this drip torch moved on Toby's east along the gravel road, creating a
headfire along the S side. (Remember that the oak savanna south of the gravel road was already black
from the burn of March 21.)

The line running along the N of Woodland Extension moved
into Unit 13B and then up (south) along the edge of the Conservancy property. The second
drip torch from this line did some interior lighting in north of Toby's Prairie and
eventually lighted the Triangle (a savanna remnant), starting at the small ravine between the
Triangle and Toby’s Annex.

Unit 13B, which is a fairly young Hill's oak and white oak woodland (around 75 years old), burned well without much interior lighting.

Stepping into the "black" to avoid the high flame height.Burning is a small prairie remnant adjacent to the Hill's oak/white oak woodlandThe prairie in the foreground had been burned 3-21-2016.The visible kestrel box had been watered to prevent it from burning.

The whole burn finished about 1 PM. We returned
to the cabin for lunch and regrouped for the wetland burn.

Wetland Burn (4
acres)

This wetland has some outstanding native vegetation but a firebreak is difficult to create because groundwater is often right at the surface. We try to burn as much as we can. Interesting species that we are trying to encourage include Turk's cap lily, turtlehead, swamp thistle, swamp milkweed, lousewort, stiff gentian, fringed gentian, and Liatris ligulostylis. There are also patches of the sedge Carex trichocarpa and cord grass (Spartina pectinata).

Mowing the wetland firebreak with the Kubota the day before the burn.

Kathie had mowed the firebreak for the wetland burn the day
before (see photo). Although the terrain is difficult and often has standing water, she managed to find a path through that was OK. At no place is
the area to be burned very wide, but it does widen out in a few places. Also,
she managed to carry the firebreak all the way to Cty F. See the map (PDF) for the location of this wetland burn.

The burn was done in two
phases, from the Barn/Crane prairie NW to Cty F and from the same point SE
toward the end of the Valley Prairie. Due to the predominantly E (and SE) direction of the
wind, we started the burn at the kestrel house end of the Crane Prairie and
moved N toward Cty F.

The whole line was wetlined using the pumper unit in the Kawasaki. In addition, there were four waters, two of whom were on the lookout for spots into the vast wetland to the south. It took about an hour to reach Cty F, with lots of
wetlining and slow careful lighting.

We then moved the whole crew plus the pumper back to the kestrel house and burned East. See photo below for this part of the burn.

Burning the wetland. The firebreak had already been wetlined.Most of the crew was busy making sure the fire did not creep across the firebreak.No spot fires occurred.

What was the fuel for the wetland burn? A lot of it was
probably sedge, some of which was Carex trichocarpa. Also grass and forbs. Very little, if any, cattails.

We finished the wetland burn around 4:15 PM. We then did some
serious mop-up on the downed black oak log mentioned above. This mop-up needed a chain saw and the pumper unit. (See photo)

A chain saw is essential for savanna burn mop-ups.This punky black oak log was a three-person job.Because it was near the edge of the burn unit, it could not be allowed to smoke.The pumper unit provided lots of high pressure water.

We have been using this custom-designed pumper unit for about 10 years.It is essential for mop-up during savanna burns.

The map (PDF download) gives a summary of all our spring burns, 88.5 acres. This does not include our burn of Black Earth Rettenmund Prairie, which will be the topic of another blog post.

Whether its climate change or just luck, this is the earliest we have been able to complete our spring burn program. (Some years our first burn has been March 29. One year we did not do our first burn until April 4.) Note that we did not burn in really "warm" weather. However, all our fuel was lush and well-cured.

Sunday, March 27, 2016

When is a "forest" a savanna?

I've dealt with this question briefly in earlier posts, but I am prompted to revisit it after coming across a paper with this title from an international group focused primarily in tropical savanna (the authors are from India, South Africa, Australia, North Carolina, England, and Germany). (See reference at end) I was struck that despite the completely different flora and geography, the underlying concepts were almost identical with those of our Midwest savannas.

The discussion in this paper begins with what is called the "savannization" of tropical forests due to logging, often followed by fires. "While such degraded forest areas...may 'look' like savannas due to low tree cover, their functional ecology in terms of which species predominate and how these communities respond to...[disturbance] is entirely different from that of true savannas."

The table here contrasts the characteristics of the savanna and forest.

Table 1 Comparison of physical environments, species
composition and traits of dominant tree species in savannas versus forests.

Habitat type

Mesic savanna

Forest

Environmental descriptors

High-light understorey

Low-light understorey

Frequently burnt

Fires rare, catastrophic

Vegetation composition

Trees

Trees

Forbs

Forbs

C4 grasses

C3 grasses

Adult trees

Architecture

Relatively shorter

Relatively taller

Narrower canopy diameter for a given basal area

Wider canopy diameter for a given basal area

Bark

Thick bark

Thin bark

Canopy

Lower specific leaf area

Higher specific leaf area

Open crowns and higher light penetration through canopy

Dense crowns and lower light penetration through canopy

Post-fire recovery of canopy either epicormic, or from
protected apical buds

Limited post-fire recovery of canopy

Saplings

Many have vertical pole-like architecture

Varied, branched and unbranched architecture

High root: shoot ratio

Low root: shoot ratio

Large underground storage

Low underground storage

Post-fire resprouting common under frequent, intense fires

Post-fire resprouting rare under frequent, intense fires

Seedlings

Rapid acquisition of resprouting ability through early
allocation to root

No obvious acquisition of resprouting ability

Persist through competition with C4 grasses and repeated
fire to sapling stage

Cannot persist through competition with grasses and
repeated fires

Reproductive strategy of tree community

No or few species are obligate seeders, reproduction
through root-suckering common

Reproduction through root-suckering

Ratnam et al. 2011.

One of the key characteristics is the presence of C4 grasses in the savannas, and C3 grasses in the forests. Given sufficient biomass (brought about by substantial rainfall) C4 grasses are highly flammable so that fire becomes a fundamental feature of a relatively humid (mesic) savanna. As the authors state, there is no need to distinguish between natural and anthropogenic fire, because anthropogenic fire has long replaced natural fire in almost all ecosystems. "What is important is that C4 grasses have high productivity, low decomposition rates,...and a fuel structure that readily carries fire and dries out rapidly in the dry season."

Because of the association with pyrogenic C4 grasses of savanna trees, they are perforce [and have evolved to be ] highly fire-tolerant. On the other hand, under mesic conditions trees associated with C3 grasses are shade tolerant and do not tolerate fire.

There is an exception in the Midwest here, since fire tolerant oaks are able to thrive under mesic conditions, provided fire occurs. As discussed by Abrams and Nowacki, in the absent of fire in eastern North America mesophication occurs and oak forests are replaced by maple, beech, basswood, and other fire sensitive trees.

The underlying concepts in Table 1 are worth detailed analysis.

Ratnam, Bond, Fensham, Hoffmann, Archibald, Lehmann, Anderson, Higgins, and Sankran. 2011. When is a 'forest' a savanna, and why does it matter? Global Ecology and Biogeography 20: 653-660.

Wednesday, March 23, 2016

After savanna burn: good time to see old-growth forest structure

On Monday March 21 2016 we had a great burn of the oak savannas at Pleasant Valley Conservancy. The next day Kathie and I returned to assess the burn coverage and take pictures. It turned out to be an excellent time to see the forest structure in all its simplicity. Before leaf out of trees and shrubs, before forbs and grass growth. The black forest floor provides an excellent contrast with the trees.

How is an old-growth forest characterized? These are the keys, as taken from the forestry literature:

Mix of young and old trees

Many fallen and decaying trees

Light gaps

Trees in various stages of decline

Wide diversity of plant species

No or only minimal past disturbance from logging or agriculture

Coarse woody debris on the forest floor

According to the experts, in Eastern United States it takes 150 years or longer to reach old-growth character. According to our minimal evidence, our white savannas are between 150-200 years old and many of our bur oaks are older than 200 years.

Sunday, March 20, 2016

Cedar invasion on hill prairies in the Midwest

A comparative survey of 1949 and present-day air photos will likely show that in our area the south- or south-west facing slopes that were once hill prairies are now red cedar (Juniperus virginiana) forests.

John Curtis (Vegetation of Wisconsin), who did not have the benefit of the last 50-60 fire-free years, called these "cedar glades". Given the lack of fire since Curtis day, it is likely that all his cedar glades no longer exist and are now close-canopy cedar forests.

To see an example of this sort of closed canopy cedar landscape, take a drive west on US 14 from Cross Plains to Black Earth. Every hill on the north side of the road (except Festge Park, which has been restored) has a dense cover of cedars in the region of the hill that was a prairie in Curtis' time.

Study these cedar-covered hills and try to imagine them burning almost every year, as they almost certainly did in 1949 (or earlier). Somebody, probably the landowner, simply lit a match.

It appears that cedar encroachment eventually reaches a tipping point, after which the whole hill prairie disappears almost in a flash. If cleared and burned quickly enough, the prairie might still be saved, but a dozen years of closed-canopy cedar forest and all prairie species are likely gone. (The cedar growth rate can be quantified by GIS from a series of air photos, using a technique that I described in detail in this paper.)

However, it is interesting that today not all south- and south-west slopes have closed canopies. Some are open enough (despite lack of fire) that Curtis would still call them "glades." Initial cedar establishment is probably a random event, depending primarily on transport of seeds by birds. And some sites may be more favorable to cedar growth than others.

Cedar hillside that has not yet closed in. 20 years ago this hill was completely open.Rocky Dell Road near US 14, east of Cross Plains, WI

In fact, it seems that not all south- or south-facing slopes even get invaded by cedar. In some cases, other woody species such as buckthorn, honeysuckle, walnut, and or elm take over. Perhaps the soil, steepness of the slope, or the aspect differs in those hills. But most south slopes in our area are cedar covered.

At Pleasant Valley Conservancy, when we started clearing the south slope in 1997, there was a scattering of cedar, and a scattering of red pine (planted by a former landowner), but large buckthorn, honeysuckle, and slippery elm were more common. (We removed 100-year old elms and lots of large buckthorns.) But there were still open areas, including two prairie remnants that were completely free of woody vegetation. It's not clear why these areas had survived, and in fact they were in such good shaped that it only took a single burn to bring them back to life. (See photos)

It is uncertain if a closed-canopy cedar hillside can be restored to prairie. Since the original prairies on these hillsides had probably been there since pre-settlement times, it is likely that there is still a seed bank. However, the initial flush of prairie growth after clearing would be from the rootstock, primarily of grasses. According to John Weaver's work in Nebraska, the rootstock of some species of grasses do not survive very long although others may survive for some years, gradually dying out. Since many of the former prairie remnants in our area have been under closed canopy and essentially in the dark for at least 50 years, it seems likely that there is little of the original prairie left. To recover prairie now will require extensive seeding.

It takes a lot of effort to restore hills with closed canopy. The best example is the Nature Conservancy's Spring Green Preserve, which has been undergoing restoration since 1971 (more than 40 years!). Kathie and I participated in large work parties at Spring Green back in the late 1990s and early 2000s. Some of these involved up to 100 people, with often 7 or 8 chain saws running simultaneously. The hills are now clear and are a great example of what can be done. And the prairies on these hills have recovered surprisingly well.

South slope prairie remnant. Bird's foot violet, lead plant, prairie dropseed,and other conservative species had survived here without help,and flourished after the area had been burned.

Another prairie remnant on the south slope. The woody vegetation surrounding this prairie is evident. (All later removed)This photo was taken in the fall after the first burn the previous spring.One burn is all it took to stimulate the growth of this great stand of Indian grass.

Sunday, March 13, 2016

Interesting prairie/savanna burn at Pleasant Valley Conservancy

We did our first burn this year on 11 March 2016. This was the earliest we have ever burned at
Pleasant Valley Conservancy, although in 2012 (the infamous drought year) we
burned on March 13. (The latest we have ever done our first burn has been 29
March.)

It doesn’t take long for the prairies and ridge-top savannas
to dry out, if the sun comes out and the humidity drops to 45-50% and the temperature
reaches 60 F. The important thing is to be ready to burn when good conditions
do come. It takes Amanda and Susan (and helpers) about a week to get
things ready. This means getting all the firebreaks ready, clearing around all
the snags and special trees, and getting all equipment ready. (My job was to
prepare and submit the spring burn plans to the DNR forester in February, and
get the go-ahead on the day of the burn.)

Burning the south-facing slope these years is a tricky task,
because the fuel is so lush. The photo shows what the slope looked like
at the end of the 2015 growing season.

South-facing slope in October 2015. This was a very good growing year and the fuel is very tall and flammable.

The three dominant grasses (big
bluestem, little bluestem, and Indian grass) are tall and lush, very burnable,
and capable of producing really high flames. Although the bur oaks are fairly
fire resistant, their upper branches are quite capable of catching on fire. Mop
up could therefore be a real problem.

The answer is to carry out the whole burn as a backburn. The
slope is steep and therefore more important than the wind, so the backburn has
to start from the top. This year we had a crew of 13, mostly hired contractors,
plus a few volunteers. Amanda ran the burn, as she has done the past three
years.

The first photo shows the start of the burn, at the top end
of the slope. We need very little water but lots of drip torches, especially to
broaden the blackline and cover all the territory. (The total area burned was
27 acres.)

Start of the burn, 11 March 2016 at the top of the ridge.

The next photo shows a later stage when most of the top
of the ridge was black and the fire line was starting to move down the hill.
People with drip torches were making sure that the whole line was on fire.

After the whole top of the unit was on fire, and the fire
breaks at both ends blackened, most of the time was taken with watching and
waiting, while the backburn moved slowly down the hill.

The next photo shows the fire line about half way down the hill.

Fire line gradually "backing" down the hill. The vehicles are being moved away.[Susan Slapnick photo]

A later photo from the bottom of the hill shows the
fire line about to put itself out as it runs out of fuel. Most of the later
stages of the burn occurred while the burn crew ate lunch, because there was nothing to
do but wait.

Fire about to put itself out at the bottom of the hill.

After lunch we burned all the planted prairies that were
adjacent to Pleasant Valley Road. These burns took place fairly quickly, as they were burned as conventional prairie burns, ending mostly as spectacular head
fires.

The next photo is a view from the top of the ridge the next day,
showing the black south slope and a couple of the planted prairies.

View from the top of the ridge showing several planted prairies that had been burned taken the day after the burn.

The final photo shows another view from the top, the day
after the burn.

The fire break is visible at the left side of the photo

Although this was not a large burn, it was a complicated
one. Because we are burning through an old-growth forest, with many venerable
trees, we are especially careful to protect their branches from catching
on fire.

In all, a very successful burn. We'll be burning the rest of our ridge-top savannas as soon as conditions permit.

Friday, March 4, 2016

What Once Was: Wisconsin's Twenty-mile Empire Prairie

Recently I have been using the original land survey plat maps to determine in detail the size and location of the Empire Prairie. This large prairie was a vast grassland north of Lake Mendota. There are only a few prairie remnants left of this fertile land, which is now almost completely subsumed by agriculture.

There were two products of the land survey from the 1830s and 1840s. The first was the original measurement establishing each township, section lines, corner posts and quarter posts (chains and links). The second product was a detailed plat map of each township derived from the original data. The plat maps were not done by the surveyors. Rather, their records were transferred to the Surveyor General's Office in Cincinnati (later Dubuque), where skilled cartographers drew plat maps based on the original data. These plat maps were quite accurately drawn, and although they mention nothing about trees, they lay out the prairies precisely. Plat maps for three townships (Arlington, Vienna, and Westport) that contain lots of pieces of the Empire Prairie are shown below.

All of the surveyor's notes and plat maps are available online, via the Wisconsin Cartographer's Office (WCO). I downloaded the relevant plat maps and brought them into Photoshop so that the handwritten notes etc. that were outside the township boundaries could be deleted. I then brought each image into GIS (ArcMap 10.2) and georeferenced it against a township shape file obtained from WCO. The prairie boundaries on each township plat map lined up fairly accurately with the boundary in the next township.

I also used a Basemap layer obtained from ArcGIS Online, which provided township names and section numbers, as well as roads, municipalities, and water bodies.

Once all 14 townships that had parts of the Empire Prairie had been loaded, I proceeded to draw the outlines of the prairie. I created a single polygon that spanned all 14 townships.

There were a few parcels within the prairie that were oak savanna, and these had been outlined by the cartographer. They are shown on the final map as inserts.

Once the outline was completed, I estimated the percent of prairie in each township. These data are shown in the table below. (The areas outside the prairie boundaries are either bur or white oak savannas. I obtained this information from a shape file created from the original surveyors records that was kindly provided to me by David Mladenoff of the UW-Madison Forest Ecology department.)

Finally, I located existing prairie remnants and located them on the map, using the topographic Basemap and 2010 air photos for the counties of Dane and Columbia. These remnants are shown as stars on the map, and their names are given in the table.

Several conclusions can be made. The total acreage of the Empire Prairie amounts to about 150,000 acres. However, the original surveyor's records show that the vegetation surrounding the prairie was primarily oak savanna, mostly bur and white oak. Because the prairie burned annually, it seems likely that the oak savannas also burned, so that the fire swept across the countryside in a continuous line. (Early settlers have described such fires.) There are no significant water bodies to block the movement of the fire. (Tiny Goose Pond is shown on the plat map.)

How close is my estimate to the historical data. The Empire Prairie was sometimes called the "twenty-mile prairie", since it was about 20 miles across. Since each township is 6 miles on a side, it is easy to see that 20 miles is not too far off.

My map shows that the prairie runs in a southwest/northeast direction. This seems reasonable, since the prevailing winds are from the west, and Lake Mendota blocks the whole south side from fire.

The existing prairie remnants are very tiny. Some are only a few acres and the largest (Westport Drumlin) is only about 16 acres. Obviously very little prairie is left. It is impressive that much of this remnant prairie has maintained itself with very little restoration work, or even very few burns.

Arlington Township
The vertical line across the middle is the route of the Military Road (Blue Mounds to Fort Winnebago; now Portage).
Goose Pond is the feature in Section 25 (extends east into Leeds Township).

Vienna Township
Note how the Military Road line connects to that of Arlington.

Westport Township

This simplified map (GIF format) is to permit fast downloading.A much larger version with roads, contours, and other features is available and can be provided.

For a nice cultural history of the Empire Prairie, see the following publication: Martha S. Engel and Andrew W. Hopkins. 1956. The Prairie and Its People. Bulletin 520, Agricultural Experiment Station, University of Wisconsin, Madison.